Scanner control means for a stored program controlled switching system



15 Sheets-Sheet l J. A. HARR ET AL SCANNER CONTROL MEANS FOR A STORED PROGRAM CONTROLLED SWITCHING SYSTEM 31. 1963 June 23, 1970 Original Filed Dec.

June 23, 1970 J, A, HARR ETAL 3,517,123

SCANNER CONTROL MEANS FOR A STORED PROGRMV CONTROLLED SWITCHING SYSTEM Original Filed Dec. 3l. 1963 13 Sheets-Sheet L;

June 23, 1970 J. A, HARR ET AL SCANNER CONTROL MEANS FOR A STORED PROGRAM CONTROLLED SWITCHING SYSTEM Original Filed Dec. 31, 1963 13 Sheets-Sheet 5 Nom.

lll)

18m Smm J. A. HARR ET AL SCANNER CONTROL MEANS RoR A sToRRu PROGRAM June 23, 1970 CONTROLLED SWITCHING SYSTEM Original Filed Dec. 251, 1963 13 Sheets-Sheet 4 @smb A man EN @sul E Illw w nmw M S2 hm In 3l ..IIJ mm3 3&9. mww @www 53N mmw N Q m i 66N @L 62 BQ 3.0? @my SS SR, xmz @m9 m j A l zomymmz. mw juz u m mnvw 6% BF? om@ new (9 m0 m9 NS mowwwu. wml: E z. mo.

J. A. HARR ETAL 3,517,123 SCANNER CONTROL MEANS FOR A STORED PROGRAM CONTROLLED SWITCHING SYSTEM 31, 1963 13 Sheets-Sheet 5 June 23, 1970 Original Filed Dec QT Emi fvwm I@ QNQm. @GMM Q vh. MQQQG QQQ Smm mm En .zum @6.0 Bm? @MES @225:8 momo 9201 0201 .5 A u oov. .6528 mH\ LHH .wmvl @GPQ NSG@ vt uw@ .gv mm SG, mumm\ Smmlo.. 5%: v. gwn @QG um Smm Smm .Saz mx @ma f wenn 9E um?. i

www?

i Bv man. n. NQS, uw E mw l lll l W "mw w93 Bmw Smm gms www EN ,womw m. .Sk

J. A. HARR ET AL SCANNER CONTROL MEANS FOR A STORED PROG June 23, 1970 RAM CONTROLLED SWITCHING SYSTEM 1963 13 Sheets-Sheet 6 Original Filed Dec. 31,

NSV

kbvh. QQQV Mvm.

June 23, 1970 J, A, HARR ETAL 3,517,123

SCANNER CONTROL MEANS FOR A STORED PROGRAM CONTROLLED SWITCHING SYSTEM Original Filed DGG- 31. 1963 15 Sheets-Sheet 7 FIG. 7

June 23, 1970 J, A, HARR ET AL SCANNER CONTROL MEANS FOR A STORED PROGRAM CONTROLLED SWITCHING SYSTEM Original Filed Dec. 31. 1963 1:5 sweets-sheet b- June 23, 1970 .A. HARR ETAT. 3,517,123 SCANNER CONTROL MEANS FOR A STORED PROGRAM CONTROLLED SWITGHING SYSTEM Original Filed Dec. 51, 1963 13 Sheets-Sheet 9 FIG. 9

TIMING CONTROL H J CLOCK INTERRUPTS EIsT DE Joes s. (cs) 5CANs (Cs) TIME COUNTER PROGRAM PROGW UPDATE TIME COUNTER I PROGRAM ^FRf5 EvERv s MILLIsECoNDs. ADDREssEs To B" DONE ACCORDING To TRE TIME, OE AT SPECIFIC LOAD APPROPRIATE PRDCRAM suPERvIsDRv MES ADDREssEs INTO PRDPER sCANs PRIORITY BUFFER.

F/G. .9A

UST 0F suPERvIsoRY I INE SCAN Jos E scANsICs) IDD suPERvIsoRv PROGRAM LD Low PRIORITY BUTTER PROGRAM INTERRDOATIDN ADDREssEs or suPERvIsoRv sERvICE ANS REQUEST BUETERICs) sCAN DNE DLDCII. DE sIxTEEN EINES AT A SCANNER TIME EOR sERvIcE ADDREssEs REQUESTS.

MEMORY LINE LOAD CONTROL June 23, 1970 J. A. HARR ET AL SCANNER CONTROL MEANS FOR A STORED PROGRAM CONTROLLED SWITCHING SYSTEM 1963 13 Sheets-Sheet 10 Original Filed Deo. 31.

June 23, 1970 J, A, HARR ET AL l 3,517,123

SCANNER CONTROL MEANS FOR A STORED PROGRAM 13 Sheets-Sheet 11 I m mJU U V me 1T e meIvTINe June 23, 1970 J, A, HARR ET AL SCANNER CONTROL MEANS FOR A STORED PROGRAM coNTRoLLED swl'rcHING SYSTEM Qriginal Filed Dec. 31. 1963 15 Sheets-Sheet l 2 13 Sheets-Sheet 1s o o o o o o o o o o o o o o 855205282351. o o o o o o o o c o o o o o no ksmzsomo @NQS xms2 .5528 9 9 mz: :Ozq-H oooN o 5&3 o o o o o o o o o o o o o @N Omo; ENDS@ 655m mzol o o NO OE: :Si n NzaEo o o oo ooo o o o zsooa (lill-'lll +2 6m 20 9-99:@ :NPH zzm E SND2 omN Nm z.

OO OO Jne 23, 1970 J. A. HARR ETAL SCANNER CONTROL MEANS FOR A STOHED PROGRAM CONTROLLED SWITCHING SYSTEM 1963 United States Patent O U.S. Cl. 179-18 13 Claims ABSTRACT F THE DISCLOSURE A program controlled telephone switching system in which lines and trunks are organized in groups corresponding to word organized information in a bulk memory The lines and trunks of each group for purposes of detecting requests for service are scanned simultaneously to generate a scanner response word. The scanner response word is combined with selected data obtained from memory to form a service request word. The selected data includes a line load control word which is selected in accordance with the system traic conditions.

The system work functions relative to the detection of requests for service for several groups of lines are performed on an overlap basis to minimize the processor time required for this function.

CROSS REFERENCES TO RELATED APPLICATIONS This is a division of copending application, Ser. No. 334,875, led Dec. 31, 1963, and relates to a communication switching system.

BACKGROUND 0F THE INVENTION The primary function of a communication switching system is the interconnection of the lines and trunks of the system in accordance with call signaling information obtained from the lines and trunks. Call signaling information includes signals emanating from equipments terminating the lines. Among the signals are those generated by an equipment change of state. Illustratively, telephone on-hook to off-hook transitions are indicative of a service request. Also, telephone off-hook to on-hook transitions are indicative of call termination. Likewise, other signals such as switchhook flashes are indicative of a desire for further attention during the course of a call, while dial pulses, TOUCH-TONE, multifrequency and voice signals are used to indicate the desired destination of a call.

In prior art electromechanical systems the detection of call signaling information is performed by large numbers of unifunctional circuits; however, with the intro duction of high speed electronic telephone switching systems the detection and interpretation of call signaling information is performed by a single or, at the most, a few electronic circuit arrangements. These electronic circuit arrangements serve to scan the lines and trunks to detect the current supervisory state of the line or trunk, to compare this state with the immediately preceding state and from this comparison derive indications of a request for service, hangup and dial pulses. In a telephone switching system subscriber lines are examined at a relatively slow rate (once every 100 milliseconds) to detect requests for service. After a request has been noted the line must be scanned more rapidly (approximately once every milliseconds) to detect dial pulses or other call signaling information. It is apparent that in large telephone othces, for example, oices serving in the order of 10,00() or more lines, the scanning of these lines and the associated trunks at even the slower rate of once per milliseconds is a formidable task. Prior art systems scan a line at a time and upon detection of a request interrupt the scanning to serve that request, whether it be a reqest for service, a request for hangup, or a request for further attention, etc.

In addition to merely detecting changes in supervisory state, the system must be organized to cope with transient emergency conditions `which bring about unusually high call origination surges. For example, upon the occurrence of a natural or other disaster in a particular locality, the telephone calling rate immediately rises to extremely high proportions since people are anxious to communicate with oflicials, friends and relatives. Such situations are most unusual and often the telephone handling capacityl of an oflice is exceeded. Unless steps are taken to cope with such extreme overload conditions, the facility of an oice may be effectively blocked and, although many subscribers are awaiting service, it is possible that substantially none of the calls can be processed.

It is an object of this invention to minimize the processor time required for the detection of requests for service from lines and trunks served by the communication switching system.

It is a further object of this invention to apply variable overload control in accordance with system traliic conditions.

SUMMARY OF THE INVENTION In accordance with this invention the communication paths, i.e., the lines and trunks of the system, are arranged in ordered groups; and the system comprises: scanning arrangements for determining the supervisory states of the groups of paths; a program controlled data processor which comprises a memory system containing sequences of program order words and data and a control arrangement for obtaining information from the memory system, for writing information into the memory system, for executing the sequences of program order words and for generating commands for controlling the scanner arrangement. The scanner arrangement in response to the scanner commands scans a particular group of paths to determine the supervisory states of the scanned paths and generates and transmits to the control arrangement a scanner response word comprising indicia representative of the supervisory states of the scanned paths. The control arrangement logically combines the scanner response word and selected data obtained from memory to forma service request word. The selected data obtained from memory comprises communication path last-look information which contains indicia dening the supervisory state of the corresponding communication paths as determined by an immediately preceding scan and a line load control word. The line load control words comprise an ordered set of words wherein ls" are discretely placed within the words to effect desired line load control functions. At times of extreme traffic overload, a line load control word which precludes service to all except certain emergency lines is employed. In the absence of an overload condition, the line load control word permits service to all lines and trunks of a group. Between these two extreme trac conditions service may be rendered to lines and trunks on a partial basis and under these conditions a series of line load control words are selectively employed during successive intervals of time to provide scrivce to successive groups of lines and trunks.

Advantageously, system functions relative to the detection of requests for service from lines and trunks served by the system are performed on an overlap basis with respect to several groups of communication paths. In the illustrative telephone switching system, the control arrangement employs a basic machine cycle having a time duration of 5.5 microseconds and the maximum rate at which the scanner arrangement commands may be transmitted is once every two machine cycles. The system functions relative to the detection of a request for service require approximately seven machine cycles. However, by means of overlap operation, communication paths may be scanned at the maximum rate at which the scanner arrange may be re-addressed. That is, communication paths are scanned at the rate of one group of paths each two machine cycles.

In accordance with one feature of this invention, the communication paths of a telephone switching system are arranged in ordered groups and the system functions relative to the detection of requests for service are performed on a group basis.

In accordance with another feature of this invention, variable line load control is employed to prevent processor overload.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. l through 6, arranged as shown in FIG. 13, are a schematic representation of a telephone switching system in accordance with this invention;

FIG. 7 is a time diagram showing the fundamental pulses employed in the control arrangement of FIGS. 4, 5 and 6;

FIG. 8 is a time diagram which illustrates the processing of three successive program order words;

FIG. 9 shows control functions of the system;

FIGS. l0 through 12, arranged as shown in FIG. 14, illustrate control functions during execution of a scanning sequence; and

FIG. shows the combining of data in accordance with this invention.

GENERAL DESCRIPTION The organization of a communication switching system in accordance with this invention is shown in FIGS. 1 through 6. FIGS. 1 and 2 show the Communication Switching Network 120, the Subscribers Stations 160 and the various trunk circuits which are located on the Trunk Frames 134 and 138. The Subscribers Stations 160 are connected to the Switching Network 120 by means of subscriber lines, and the trunk circuits of the Trunk Frames 134 and 138 are connected by means of trunks to the Switching Network 120 via the Trunk Distributing Frame 133. FIG. 2 further shows the Central Pulse Distributor 143, the Master Scanner 144, the Teletypewriter 145 and the Program Store Card Writer 146. The Central Pulse Distributor 143 is a high speed electronic translator which, in response to pulse distributor commands from the Control Arrangement 101 over the Conductor Group 107, provides short duration pulses for controlling various elements of the communication switching system.

The Master Scanner 144 responds to commands from the Control Arrangement 101 of FIGS. 4 through 6 to detect the states of various equipments in the system.

The Teletypewriter 145 is employed by the ofi-lee personnel to insert new information into the communication switching system and to obtain administrative information generated by the system.

The Program Store Card Writer 146 is a mechanism for preparing new information cards for the Program Store 102.

In FIG. 3 there is shown a Line Scanner 123. In the illustrative embodiment, the Subscribers Lines 160 are arranged in ordered groups of sixteen lines per group for purposes of scanning. This grouping of communication path circuits is shown in the Ferrod Matrix 9960 of FIG. 3. In this figure there are shown two of a plurality of horizontal rows of ferrods. The rst row comprises ferrods 0000 through 0015 and the last row comprises ferrods 6300 through 6315. The scanner of FIG. 3 is arranged to accept command signals from the Central Control 101 of FIGS. 4, 5 and 6 and to interrogate a particular row of ferrods indicated by the command. The Scanner 123 generates a scanner response word wherein there is discrete indicia representative of the supervisory state of each line of a group of lines. The scanner response word is generated in the Scanner Control and Drive Circuits 302 of FIG. 3 and is transmitted to the Central Control 101 via the Conductor Group 108. Information on Conductor Group 108 is transmitted through the Gate Circuits 1400 to the Logic Register 2508.

The Central Control 101 selectively obtains related data from the Call Store 103 and this data is returned to the Buffer Register 2601 via the Conductor Group 6501 and the Gate Circuits 2102. In accordance with the invention, the selected related data comprises at least a last-look word. The last-look word in the illustrative embodiment is a 23-bit data word wherein the rightmost sixteen bit positions contain indicia representative of the supervisory states of the related group of lines as determined by the immediately preceding scan of those lines. The left seven bit positions of the last-look word cornprise the seven least significant address bits for the next scanner row. For example, if the last-look word shows the busy-idle states of the communication paths of row X, the address accompanying this word will comprise the seven least significant bit positions of the address of scanner row X-I-l.

The Central Control 101 is arranged to control the Circuit 2000 and internal gating of the Central Control 101 to combine the contents of the LR Register 2508 and the contents of the Bulfer Register 2601 in the Circuit 2000. The combining of data in accordance with this description is illustrated in FIG. 15. In the illustrative example a 1 in a `bit position of the last-look Word indicates that the corresponding line was found to be in the off hook supervisory state during the preceding scan. A 1 in a bit position of the scanner answer word, however, indicates that the lines scanned are in the on hook state. These words, namely, scanner answer word and the last-look word are combined in the Circuit 2000 by the logical function OR and the resulting word is complemented. As shown in the illustrative figure, the resulting service request word comprises a 1 in each bit position wherein a line has experienced a change from the on hook to the off hook state between successive scans. The resulting word is transmitted via the Bus 2011 and the K Logic Circuitry 3505 to the K Register 4001.

The contents of the K Register 4001 are examined by means of the Detect First l Circuit 5415. The Detect First 1 Circuit 5415 generates an output word which identifies the rightmost 1 in the resulting data word and then resets that bit position in the K Register 4001 to the 0 state. Each successive 1" in the resultant data word is thus identified. The identity of the rightmost position is combined with other information available in the Central Control to provide a data word which fully identifies each communication path which is requesting service. This identity comprises the particular position in the ordered group, the identity of the ordered group and the identity of the scanner serving that ordered group. This identity is transmitted under program control to the Buffer Register 2601 for subsequent insertion in a buffer area in the Call Store 103. Subsequently, other program sequences employ this data to provide service for the requesting lines.

A second element of data which may be selectively obtained from the Call Store 103 are the line load control masking words. The line load control masking words are also selectively merged with the scanner answer word and the last-look word to form a modified service request data word. The line load control mask words comprise an ordered set of words wherein ls are discretely placed within the words to effect a desired line load control function. At times of extreme traffic overload, a line load control mask word which precludes service to all except certain emergency lines will be employed. In the absence of an overload condition, the line load control word serves no function and does not preclude service to any particular line or group of lines. Between these two extreme conditions service may be rendered on a partial basis and in these conditions a series of line load control mask words are employed during successive intervals of time to provide partial service to successive groups of subscribers.

A line load control mask word comprises a series of ls and Os in bit position through 15. A 1 occurs in the bit positions to which service is permitted and a 0 in those bit positions to which service is precluded. The combining of the service request word and the line load control mask word by the function of logical AND results in a line load control service request word wherein a l occurs in each bit position assigned to a requesting line to which service is permitted.

COMMUNICATION BUSES AND CABLES Communications between major divisions of this system are by way of bus systems and by way of multiple conductor cables which provide discrete communication paths between selected divisions of the system. The buses and cables are detailed later herein.

Communication within a major division of this system, such as a Central Control 101, may be by way of bus systems; however, such internal bus systems comprise a plurality of single rail parallel paths and are not intended to be covered by the following discussion.

A bus system, as dened herein, comprises a plurality of pairs of conductors. A bus is a transmission means for transferring information from one or more sources to a plurality of destinations. A bus is transformer coupled to both the information source or sources and to the destination loads. The information sources are connected to the bus conductors in parallel and the loads are coupled to transformers which are serially connected in the bus conductors.

Data transmitted over a bus is in pulsed form and in this particular embodiment extremely short pulses in the order of one-half microsecond are transmitted. Information on a bus system is transmitted in parallel, that is, a data word or a command is transmitted in parallel over the plurality of pairs of conductors of the bus and it is important that such parallel data elements arrive at a given load equipment at a common time. Accordingly, the pairs of conductors of a bus system are arranged to follow similar physical paths and their lengths are kept substantially identical.

In addition to the bus systems there are a plurality of multiple conductor cables which provide discrete communication paths between selected divisions of the switching system. The conductor pairs of these cables are in many instances transformer coupled both to the information source and the destination load; however, there are also a number of cables wherein D-C connections are made to both the source and the destination load.

While a bus is a unidirectional transmission means, there are specific instances wherein a cable pair comprises a bidirectional transmission means.

SWITCHING NETWORK (120) The Switching Network 120 serves to selectively interconnect through metallic paths lines to lines via junctor circuits, lines to trunks, trunks to trunks, lines and trunks to tones, signal transmitters, signal receivers, maintenance circuits, and, in the case of lines, to provide connections to coin supervisory circuits, et cetera. Two-wire paths between the above enumerated equipments are provided through the network of this one specific illustrative embodiment.

The Switching Network 120 only provides communication paths, means for establishing such paths and means for supervising such paths. The Central Processor maintains a record of the busy and idle states of all network links and a record of the make-up of every established or reserved path through the network. These records are maintained in the Call Store 103 of the Central Processor 100. The record relating to the busy-idle states of the network elements is generally referred to as the Network Memory Map. The Central Processor 100 interprets requests for connection between specific pieces of equipment and determines a free path through the network by examining the connection requirements and the above-noted busy-idle states of the possible paths.

The network is divided in two major portions, namely, line link networks which terminate lines and junctors (both wire junctors and junctor circuits) and the trunk link networks which terminate trunks and wire junctors, service circuits such as tone circuits, signal receivers, signal transmitters, et cetera. A line link network comprises four switching stages, the rst two stages of which are concentrating stages, while a trunk line network comprises four stages generally without concentration. In this one specific illustrative embodiment there is a single path provided between a line and each of a plurality of line link network junctor terminals. There are four paths through a trunk link network between a trunk terminal and each of a plurality of trunk link network junctor terminals.

Certain junctor terminals of each line link network are connected directly through wire junctors (a pair of wires without other circuit elements) to certain junctor terminals of the trunk link networks; others of the line link network junctor terminals are interconnected either by way of junctor circuits (which provide talking battery and call supervision facilities) or, in very large offices, by way of junctor circuits and additional stages of switching.

Junctor terminals of a trunk link network which are not connected to junctor terminals of a line link network are directly interconnected by wire junctors or, in extremely large oiliees, by way of' wire junctors and additional switching stages.

Control of the network and the control and supervision of the elements connected to the network are distributed through a number of control and supervisory circuits. This disbursement provides an efficient and convenient buffer between the extremely high speed Central Processor 100 and the slower network elements. The principal control and supervisory elements are:

(l) The network control circuits which accept commands from the Central Processor 100 and, in response to such commands, selectively establish portions of a selected path through the network or, in response to such commands, execute particular test or maintenance functions.

(2) The network scanners which comprise a ferrod scanning matrix to which system elements such as lines, trunks and junctor circuits are connected for purposes of observing the supervisory states of the connected elements; the network scanners, in response to commands from the Central Processor 100, transmit to the Central Processor 100 indications of the supervisory states of a selected group of circuit elements.

(3) The network signal distributors which, in response to commands from the Central Processor 100, provide an operate or a release signal on a selected signal distributor output terminal which is termed herein a signal distributor point. A signal of a first polarity is an operate signal and a signal of the opposite polarity is a release signal. Signal distributor output signals are employed to operate or release control relays in junctor circuits, trunk circuits, and service circuits. A magnetically latched wire spring relay is used generally throughout the junctor circuits and trunk circuits for purposes of completing the transmission paths through these elements and for circuit control in general. The magnetically latched relay operates in response to an operate signal (-48 v.) from a signal distributor and releases in response to a release signal (+24 v.) from a signal distributor. The network signal distributors are relatively slow operating devices in that they comprise pluralities of relays. Signal distributor output signals are pulsed signals and a single signal distributor can be addressed to only one of its output points at any given instant.

Of the three above-noted network control and supervisory elements (there are pluralities of each of these) the network controllers and the signal distributors are relatively slow operating devices and to assure completion of a task, each of these devices is addressed at the maximum repetition rate of once every 25 milliseconds. This period of time is sufficient to assure completion of the work function associated with a network controller or signal distributor command. Therefore, there is no need for the Central Processor 100 to monitor these devices to assure completion of their assigned tasks before transmitting a subsequent command to the same controller. However, to assure continued trouble free operation scan points which reflect the successful completion of a preceding order are examined before sending a new command to the controller. The network scanners, however, are relatively fast operating devices and these may be addressed at a maximum rate of once every l1 microseconds.

SUBSCRIBER CIRCUITS The subscriber sets such as 160, 161 are standard sets such as are employed with present day telephone switching systems. That is, these are sets which connect to the central ofiice via a two-wire line, respond to normal 20 cycle ringing signals and may be arranged to transmit either dial pulses or TOUCH-TONES or may be arranged for manual origination. Subscriber stations comprising one or more subscriber sets such as 160, 161 all terminate at line terminals of a line link network. A subscriber line may have either TOUCH-TONE sets or dial pulse sets or combinations of TOUCH-TONE and dial pulse sets. Information concerning the type of call signaling apparatus associated with a subscribers line is included in the class of service mark which is maintained normally in the Program Store 102; however, after a recent change this information is found in whole or part in the Call Store 103.

Supervision of a subscribers line is by way of the line scanners which are located in the vicinity of a line link network. Such scanners, however, are generally employed only to detect requests for service. After a request for service has been served and a subscribers line has been connected through the network to a trunk or to a service circuit such as a subscribers dial pulse receiver, subscribers TOUCH-TONE receiver, a tone source, et cetera, or to another subscriber via a junctor circuit, the scanning element associated with a subscribers line is disconnected and subsequent supervision for answer and disconnect is transferred either to the trunk, the service circuit, or the junctor circuit. The subscribers line scanning element is reconnected only after the subscribers line has been released from the prior connection.

Service circuits such as subscriber call signaling receivers and subscriber information tone sources such as busy tone, ringing tone, ringing induction tone, recorded announcements, vacant level tone, et cetera, are terminated at trunk terminals of the trunk link network. Connections between a subscribers station and a service circuit such as a dial pulse receiver or a TOUCH-TONE receiver and connections between a subscribers set and a tone source include the four stages of a line link network and the four stages of a trunk link network.

Communication with a distant oliice or an operator is by way of two-way trunks, outgoing trunks, incoming trunks, operator trunks, et cetera, which are located in the Trunk Frames 134, 138 and which all terminate at trunk terminals of a trunk link network. In the case of a call `between a subscribers station and a trunk or service circuit, talking battery to the subscriber is provided through the trunk or service circuit and supervision for disconnect is accomplished by scanning the scanning elements of the connected trunk or service circuit.

CENTRAL PULSE DISTRIBUTOR (143) The Central Pulse Distributor 143 is a high speed electronic translator which provides two classes of output signals in response to commands from the Central Processor 100. The two classes of output signals are termed unipolar signals and bipolar signals and are respectively associated with central pulse distributor output terminals designated CPD unipolar points and CPD bipolar points. Both classes of signals comprise pulses transmitted from the CPD output points to the using devices via individual transmission pairs which are transformer coupled both to the CPD output points and to the load devices.

Central pulse distributors for purposes of reliability are employed in pairs and corresponding bipolar output points of the two central pulse distributors of a pair are employed to address the same circuit element. Similarly, unipolar points are associated in pairs to accomplish related system functions.

The address coding associated with each central pulse distributor is suicient to dene 1,024 CPD points. Of these 1,024 points, 512 are assigned to unipolar points while the other 512 are assigned to 256 pairs of bipolar points.

The most common use of the unipolar signals is to momentarily enable a particular piece of equipment such as a Network Controller 122, a Network Scanner 123, et cetera. The enablement signals comprise relatively important information; therefore, in response to an enablement signal the enabled circuit, shortly after the receipt thereof, transmits a verify signal lback to the Central Pulse Distributor 143 over the same pair that was used to transmit the enable signal. The verify signal is received at the Central Pulse Distributor 143 and is translated to the same form as the address portion of the command which was transmitted from the Central Control 101 to the Central Pulse Distributor 143. The translated verify signal is transmitted to the Central Control 101 where it is compared against the address which was transmitted. A match assures enablement of the correct unit of equipment. Not all unipolar output signals represent information `which is as important as the enable signals; therefore, certain unipolar signals are not verified.

Both unipolar output signals and bipolar output signals comprise pulses and, as in the case of the signal distributors, only one CPD output point, either unipolar or bipolar, can be enabled at any given instant. Unipolar output signals while generally employed to provide transient gating signals to enable the receiving circuit are also used to set and reset flip-hops in particular instances. Bipolar output signals are employed to both selectively set and reset flip-flops at the receiving circuits. A bipolar signal is accompanied by a WRMI security signal when employed to control certain critical circuits. A signal of the first polarity serves to set a flip-flop and a signal of the other polarity serves to reset a tlip-op. The system generally has means for verifying the setting or resetting of a flip-flop in response to CPD bipolar signals; therefore, bipolar signals are not directly verified in the manner employed in the case of unipolar signals.

The Central Pulse Distributor 143 is an electronic device; therefore, its output signals are employed to control other relatively high speed circuits. For example, central pulse distributor output signals are employed to control the sending of both multifrequency signals and dial pulses from a switching center to a distant office via a trunk circuit and central pulse distributor output points are also employed to set or reset control ip-tlops in a variety of system equipments, Generally these control flip-flops must be set or reset at speeds which approach a basic system instruction cycle; therefore, the slow speed signal distributor output signals are not adequate.

MASTER SCANNER (144) The Master Scanner System 144 comprises a ferrod matrix for terminating circuits to be supervised and means for selectively transmitting to Central Control 101 the supervisory states of a selected group of supervised circuits in response to a command from the Central Processor 100. The scanners employed herein are described in greater detail in copending U.S. patent application A. M. Guercio-H. F. May, Ser. No. 250,416, filed l' an. 9, 1963. The scanning element employed is the ferrod device which is disclosed in the copending application of J. A. Baldwin, Ir.- H. F. May, Ser. No. 26,758, led May 4, 1960. A ferrod comprises an apertured stick of ferromagnetic material having control, interrogate, and readout windings. The control windings are placed in series with electrical connections which indicate the supervisory state of the supervised circuit. For example, where a ferrod is employed to supervise a subscribers line, the ferrod is placed in series with the line conductors andthe subscribers subset. When the subscribers su'bset is in the on-hook state there is no current flowing in the ferrod control winding, while when the subscriber is in the offhook state current does flow in the ferrod control winding. The interrogate and readout rwindings merely comprise individual conductors which thread through the two apertures of the ferrod, that is, both the interrogate conductor and the readout conductor are threaded through both apertures of the ferrod. An interrogate signal comprises a bipolar pulse which when applied to the interrogate conductor causes an output signal in the readout conductor of every ferrod which is supervising a circuit which is in the on-hook state. If the ferrod is supervising a circuit in the off-hook state, a readout pulse is not generated due to saturation of the ferrod.

The Master Scanner System 144 comprises one or more scanners each capable of supervising 512 circuits. The scanners of the Master Scanner 144 are not duplicated; however, there is a complete duplication of access circuity within a scanner to provide system reliability. The Master Scanner 144 is generally like the Network Scanners (123, 127, 135, 139) which are distributed through the network frames; however, the Master Scanner 144 is employed to supervise certain circuit elements which retiect the operating state of the system and, therefore, the supervisory states of these elements are helpful in system maintenance and trouble diagnosis. For example, scan points of the Master Scanner 144 are employed to monitor the voltage levels of critical voltage supplies, and the states of control relays and logic packages such as flip-flops to assure proper operation thereof. In addition, the Master Scanner 144 is employed to monitor a few circuits which terminate on the Switching Network 120 and which for efficiency of grouping are more conveniently examined by way of the Master Scanner 144.

LINE SCANNER (123) (FIG. 3]

The following discussion is directed specifically to the Line Scanner 123 which is arranged to supervise 1,024 circuits.

A scanner comprises an unduplicated ferrod matrix and duplicated control and drive circuitry for interrogating the matrix. The Control Circuits 302 serve to accept information from the Network Command Bus System 104, to regulate timing of actions within the scanner and to gate information derived from the Ferrod Matrix 9960 back to the Central Control 101 via the Scanner Answer Bus System 108. The drive circuits are employed to selectively interrogate the rows of the Ferrod Matrix 9960 in accordance with the address information which is received from central control via the Network Command Bus System 104..

In the normal mode of operation information concerning the supervisory state of a particular designated group of sixteen supervised circuits is returned to the central control via the Scanner Answer Bus System 6600.

The scanners are unlike both the Program Store 102 and the Call Store 103 in that each of the scanners is selectively enabled by means of central pulse distributor unipolar output signals on conductor 301.

Enable and command information is transmitted to a scanner in two waves and, similarly, verify and scanner answer information is transmitted from the scanner to Central Control 101 in two waves. An enable signal is received at a scanner and after approximately three-quarters of a microsecond beyond the start of the enable signal the scanner address is received.

The interrogate conductors of the core matrices such as conductors F00 and FR00 are threaded through the interrogate windings of the ferrods of a row. As shown in FIG. 3 the conductor F00 is in series with the interrogate windings of the odd numbered ferrods of the iirst row, while the conductor FR00 is in series with the interrogate winding of the even numbered ferrods of the first row and the conductors F00 and FR00 are terminated in a resistor and the primary of a transformer such as ASWT-l).

Each row of ferrods of the Matrix 9960I includes a transformer such as ASWT-ll and ASWT-63. A signal is induced in a transformer such as ASWT-0 when the row of ferrods associated therewith is interrogated by a core matrix signal. Signals induced in the secondaries of these transformers are employed as input signals to the 0R gate 9961 the output of which comprises a check signal which is transmitted to the Central Control 101.

The output windings of the ferrods of a column are connected in series with each other and in series with a secondary winding of a test transformer such as MTD. These conductors such as R00 and RR00 comprise input signals to the scanner answer AND gates in the Scanner Control 302.

The scanner responses which result from the interrogation of the ferrods of the Matrix 9960 are transmitted through these AND gates to the Central Control 101.

CENTRAL PROCESSOR The Central Processor 100 is a centralized data processing facility which comprises:

( l) Program Store 102; (2) Call Store 103; (3) Central Control 101.

Program Store (102) The Program Store of the Central Processor comprises a plurality of indepedent memory units which are passive in the absence of commands from the Central Control.

In the illustrative embodiment, the Program Store is a permanent magnet-magnetic wire memory (Twistor) which affords nondestructive readout of the information stored therein in response to response to commands from the Central Control 101. The Program Store, being semipermanent in nature, is employed to store certain system data, which is changed only at relatively long intervals, and the system programs. Information is written into the Program Store by means of the Program Store Card Writer 146 (FIG. 1) under commands from the Central Control 101.

- 11 can store (10s) The Call Store of the Central Processor comprises a plurality of independent memory units.

The Call Store, like the Program Store, is passive in the absence of commands from the Central Control,

In the illustrative embodiment, a word organized ferrite sheet memory is employed as the memory element of the Call Store 103. The Call Store is a destructive readout type memory and information may be read from or written into this memory in a time cycle which corresponds to the time cycle of the Central Control 101. The Call Store, being temporary in nature, is employed to store the system data which is subject to rapid change in the course of processing calls through the system.

CENTRAL CONTROL (101) [FIGS 4-61 The central control performs system data processing functions in accordance with program orders which are stored principally in the Program Store 102. In a few specialized instances program orders are found in the Call Store 103. The program orders are arranged within the memories in ordered sequences. The program orders fall into two general classifications, namely, decision orders and nondecision orders.

Decision orders are generally employed to institute desired actions in response to changing conditions either with regard to lines or trunks served by the switching system or changing conditions with respect to the maintenance of the system.

Decision orders dictate that a decision shall be made in accordance with certain observed conditions and the result of the decision causes central control to advance to the next order of the current sequence of order words or to transfer to an order in another sequence of order words. The decision to transfer to another sequence may be coupled with a further determination that the transfer shall be made to a particular one of a plurality of sequences. Decision orders are also termed conditional transfer orders.

Nondecision orders are employed to communicate with units external to Central Control 101 and toboth move data from one location to another and to logically process the data. For example, data may be merged with other data by the logical functions of AND, OR, EXCLUSIVE- OR, product mask, et cetera, and also data may be complemented, shifted, and rotated.

Nondecision orders perform some data processing and/or communicating actions, and upon completion of such actions most nondecision orders cause the Central Control 101 to execute the next order in the sequence. A few nondecision orders are termed unconditional transfer orders and these dictate that a transfer shall be made from the current sequence of program orders to another sequence of order words without benefit of a decision.

The sequences of order words which are stored principally in the program store comprise ordered lists of both decision and nondecision orders which are intended to be executed serially in time. The processing of data within the central control is on a purely logical basis; however, ancillary to the logical operations, the Central Control 101 is arranged to perform certain minor arithmetic functions. The arithmetic functions are generally not concerned with the processing of data but, rather, are primarily employed in the process of fetching new data from the memories such as from the Program Store 102, the Call Store 103, or particular flip-flop registers within the Central Control 101.

The Central Control 101, in response to the order Word sequences, processes data and generates and transmits signals for the control of other system units. The control signals which are called commands are selectively transmitted to the Program Store 102, the Call Store 103, the Central Pulse Distributor 143, the Master Scanner 144, the network units such as the Network Scanners 123, 127, 135, 139, Network Controllers 122, 131, Network Signal Distributors 128, 136, 140, and the miscellaneous units such as the Teletype Unit 145, the Program Store Card Writer 146, and the AMA Unit 147.

The Central Control 101 [FIGS 4-6] is, as its name implies, a centralized unit for controlling all of the other units of the system. A Central Control 101 principally comprises:

(A) A plurality of multistage flip-Hop registers;

(B) A plurality of decoding circuits;

(C) A plurality of private bus systems for communicating between various elements of the central control;

(D) A plurality of receiving circuits for accepting input information from a plurality of sources;

(E) A plurality of transmitting circuits for transmitting commands and other control signals;

(F) A plurality of sequence circuits;

(G) Clock sources; and

(H) A plurality of gating circuits for combining timing pulses with D-C conditions derived within the system.

The Central Control 101 is a synchronous system in the sense that the functions within the Central Control 101 are under the control of a multiphase Microsecond Clock 6100 which provides timing signals for performing all of the logical functions within the system. The timing signals which are derived from the Clock 6100, 6101 are combined with D-C signals from a number of sources in the Order Combining Gate Circuit 3901. The details of the Order Combining Gate Circuit 3901 are not shown in the drawing as the mass of this detail would ymerely tend to obscure the inventive concepts of this system.

Sequence of Central Control Operations All of the system functions are accomplished by execution of the sequences of orders which are obtained from the Program Store 102 or the Call Store 103. Each order of a sequence directs Central Control 101 to perform one operational step. An operational step may include several logical operations as set forth above, a decision where specified, and the generation and transmission of commands to other system units.

The Central Control 101 at the times specified by phases of the Microsecond Clock 6100 [FIG. 5] performs the operational step actions specified by an order. Some of these operational step actions occur simultaneously within Central Control 101, while others are performed in sequence. The basic machine cycle, which in this one illustrative embodiment is 5.5 microseconds, is divided into three major phases of approximately equal duration. For purposes of controlling sequential actions within a basic phase of the machine cycle each phase is further divided into one-half microsecond periods which are initiated at one-quarter microsecond intervals.

The basic machine cycle for purposes of designating time is divided into one-quarter microsecond intervals, and the beginning instants of these intervals are labeled T0 through T22. The major phases are labeled phase 1, phase 2, and phase 3. These phases occur in a 5.5 microsecond machine cycle as follows:

(A) Phase 1T0 to T8, (B) Phase 2-T10 to T16, (C) Phase 3-T16 to T22.

For convenience in both the following description and in the drawing, periods of time are designated bTe where b is the number assigned the instant at which a period of time begins and e the number assigned the instant at which a period of time is ended. For example, the statement T16 denes phase 2 which begins at time 10 and ends at time 16. The division of time is shown in FIG. 7.

In order to maximize the data processing capacity of Central Control 101 three cycle overlap operation is employed. In this mode of operation central control simultaneously performs:

(A) The operational step for one instruction;

(B) Receives from the Program Store 102 the order for the next operational step; and

(C) Sends an address to the Program Store 102 for the next succeeding order.

This mode of operation is illustrated in FIG. 8. Three cycle overlap operation is made possible by the provision of both a Butler Order Word Register 2410, an Order Word Register 3403 and their respective decoders, the Buffer Order Word Decoder 3902 and the Order Word Decoder 3904. A Mixed Decoder 3903 resolves conicts between the program words in the Order Word Register 3403 and the Buffer Order Word Register 2410. The Auxiliary Buffer Order Word Register 1901 absorbs differences in time of program store response.

The initial gating action signals for the order X (herein designated the indexing cycle) are derived in the Buffer Order Word Decoder 3902 in response to the appearance of order X in the Buffer Order Word Register 2410. The order X is gated to the Order Word Register 3403 (while still being retained in the Buffer Order Word Register 2410 for the indexing cycle) during phase 3 0f cycle 2; upon reaching the Order Word Register 3403 the nal gating actions (herein indicated as the execution cycle) for the order X are controlled via Order Word Decoder 3904.

The indexing cycle and the execution cycle are each less than a 5.5 microsecond machine cycle in duration. In the executing of the operational steps of a sequence of orders like those shown in FIG. 8 each order remains in the Order Word Register 3403 and the Buffer Order Word Register 2410 each for one 5.5 microsecond cycle. The Buffer Order Word Decoder 3902 and the Order Word Decoder 3904 are D-C combinational circuits; the D-C output signals of the decoders are combined with selected microsecond clock pulses (among those indicated in FIG. 7) in the Order Combining Gate Circuit 3901. This Order Combining Gate Circuit 3901 thus generates the proper sequences of gating signals to carry out the indexing cycle and the execution cycle of each of the sequence of orders in turn as they appear first in the Buffer Order Word Register 24.10 and then in the Order Word Register 3403.

The performance of the operational steps for certain orders requires more time than one operational step period, Le., more than 5.5 microseconds. This requirement for additional time may be specified directly by the order; however, in other instances this requirement for additional time is imposed by indicated trouble conditions which occur during the execution of an order. Where an order specifies that the execution thereof will require more than one operational step period, the additional processing time for that order may be gained by:

(l) Performing the additional data processing during and immediately following the indexing cycle of the order and before the execution cycle of the order; or

(2) Performing the additional data processing during and immediately after the normal execution cycle of the order.

The performance of these additional work functions is accomplished by way of a plurality of sequence circuits within Central Control 101. These sequence circuits are hardware configurations which are activated by associated program orders or trouble indications and which serve to extend the time in the operational step beyond the normal operational step period illustrated in FIG. 8. The period of time by which the normal operational step period is extended varies depending upon the amount of additional time required and is not necessarily an integral number of machine cycles. However, the sequences which cause delays in the execution of other orders always cause delays which are an integral number of machine cycles.

The sequence circuits share control of data processing within the Central Control 101 with the decoders, i.e., the Buffer Order Word Decoder 3902, the Order Word Decoder 3904, and the Mixed Decoder 3903. In the case of orders in which the additional work functions are performed before the beginning of the execution cycle, the sequence circuit, or as more commonly referred to, the sequencer controls the Central Control 101 to the exclusion of decoders 3902, 3903, and 3904. However, in the case of orders in which the additional work functions are performed during and immediately after the execution cycle of the order, the sequencer and the decoders jointly and simultaneously share control of the Central Control 101. In this latter case there are a number of limitations placed on the orders which follow an order which requires the enablement of a sequencer. Such limitations assure that the central control elements which are under the control of the sequencer are not simultaneously under control of the program order words.

Each sequence circuit contains a counter circuit, the states of which define the gating actions to be performed by the sequence circuit. The activation of a sequence circuit consists of starting its counter. The output signals of the counter stages are combined with other information signals appearing within Central Control 101 and with selected clock pulses in the Order Combining Gate Circuit 3901 to generate gating signals. These signals carry out the required sequence circuit gating actions and cause the counter circuit to advance through its sequence of internal states.

Sequence circuits which extend the period of an operational step by seizing control of a Central Control 101 to the exclusion of the decoders 3902, 3903 and 3904 are arranged to transmit the address of the next succeeding program order word concurrently with the completion of the sequencer gating actions. Thus, although the execution of the order immediately succeeding an order which enabled the sequencer of the above character is delayed, the degree of overlap shown in FIG. 8 is maintained.

Sequence circuits which do not exclude the decoders 3902, 3903 and 3904 provide additional overlap beyond that shown in FIG. 8. That is, the transmission of the address of and acceptance of the order immediately succeeding an order, which enabled a sequencer, are not delayed. The additional gating actions required by such sequence circuits are carried out not only concurrently with the indexing cycle of the immediately succeeding order, but also concurrently with at least a portion of the execution cycle of the immediately succeeding order.

A few examples will serve to illustrate the utility of the sequence circuits. A program order which is employed to read data from the Program Store 102 requires an additional two 5.5 microsecond machine cycle periods for completion. This type of order gains the additional two cycles by delaying the acceptance of the immediately succeeding order and performs the additional work operations after termination of the indexing cycle of the current order and before the execution cycle of the current order.

When errors occur in the reading of Words from the Program Store 102, the Program Store Correct-Reread Sequencer 5301 is enabled to effect a correction or a rereading of the Program Store 102 at the previously addressed location. This sequence circuit is representative of the type of sequence circuit which is enabled by a trouble indication and which seizes control of the Central Control 101 to the exclusion of the decoders.

The Command Order Sequencer 4902 which serves to transmit network commands to the Switching Network 

